U.S. Pat. No. 3,581,733 describes a system for continuously infusing a parenteral liquid, such as normal saline, into a patient at a very slow flow rate while blood pressure is continuously monitored through a pressure transducer and measuring device. This continuous infusion at a very slow flow rate is to prevent blood from entering the system and coagulating, thus interferring with a hydraulic pressure wave being sent to the pressure transducer. Periodically it is necessary to flush the system with a faster flow rate of normal saline. This is done with a stopcock 18 which transfers flow from a restricted passage 16 to a much larger passage 14, as schematically shown in the drawings of U.S. Pat. No. 3,581,733.
Another U.S. Pat. No. 3,675,891 discloses a similar system for continuously administering parenteral liquid to a patient while monitoring blood pressure fluctuations. However, this patent describes a flushing valve with an elastic pull stem. If the valve is located in a flexible line, this requires a two handed operation; i.e., one hand to hold the valve, and one to pull the stem. Enclosed is an instruction sheet for the device of U.S. Pat. No. 3,675,891 showing its use. Even if the valve is attached to a rigid pressure transducer on a supporting pole, an overly aggressive pull on the stem could upset the supporting pole, etc.